Affecting a Carboxy Group

Carboxytellurophenes were esterified, reduced by lithium aluminum hydride, converted to amides, and decarboxylated. Esters of carboxytellurophenes were saponified. Esterification of carboxytellurophenes with diazomethane produced methoxy- 

Treatment of 2-carboxytellurophene or of 2-methoxycarbonyltellurophene with lithium aluminum hydride in diethyl ether at 0° yielded 2-hydroxymethyltellurophene.  

Heating 2-carboxytellurophene with hexamethylphosphoric acid triamide at 180° yielded N,N-dimethylaminocarbonyltellurophene.  

2-Carboxytellurophenes were decarboxylated upon heating in quinoline in the presence of copper powder d or copper chromite.  

Alkoxycarbonyltellurophenes were hydrolyzed to the free carboxylic acids in basic as well as in acidic media s. 

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Through Modification of Substitutents 3.2.1. Affecting a Carboxy Group... 

Stearic acid and oleic acid are fatty acids, compounds that contain a carboxy group (COOH) attached to the end of a long carbon chain. Stearic acid is a saturated fatty acid because each carbon atom in its long chain has the maximum number of bonds to hydrogen. Oleic acid is an unsaturated fatty acid because its carbon chain contains one (cis) double bond. The presence of a double bond greatly affects the chemical and physical properties of these fatty acids. In Chapter 10 we learn about alkenes, organic compounds that contain carbon-carbon double bonds. 

Since amide bond formation is a bimolecular reaction which involves a nucleophUic attack of the amino group on the activated carboxy group (Scheme 1), the kinetics are strongly affected by the type of carboxy activation, by steric effects exerted by the involved reaction partners, as well as by the solvents and catalysts employed (for comprehensive reviews, see refst ). Moreover, the concentration of the reactants plays a critical role and excess of one of the two components serves to drive the reaction to completion. 

The action pattern and kinetics of a dextranase obtained from Penicillium funiculosum have been studied. Whereas chelated cobalt compounds did not activate the enzyme, Co + ions and cobalt species bound by the enzyme enhanced its activity, with a concomitant decrease in the activation energy and an increase in l x Km was not affected. From modifications to L-lysine, L-arginine, L-histidine, and L-cysteine residues and carboxy-groups in the enzyme, it was concluded that an L-cysteine residue located outside the active site is responsible for the activation. It appears that conformational changes induced when cobalt ions combine with this amino-acid residue make it easier for the enzyme to accept dextran and for the enzyme-substrate complex to dissociate. 

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